INTRODUCTION TO A NEW INSPIRATORY THRESHOLD LOADING DEVICE

Inspiratory threshold loading is an important tool in assessing inspir atory muscle function and has been widely used in studies of respirato ry mechanics. A simple system was designed to provide a pure and preci se inspiratory threshold load. The inspiratory threshold loading syste m comprises a Row generator attached via a pressure chamber, to the in spiratory port of a Hans-Rudolph valve. By limiting the circulation of air generated by the Bow generator between the room and the pressure chamber, different levels of negative pressure are produced in the pre ssure chamber and applied to the inspiratory valve, An inspiratory pre ssure equal to the negative pressure in the chamber has to be generate d to open the inspiratory valve for Bow, The system was tested in four subjects by measuring mouth pressure (Pm), threshold pl.ess;re (Pth) and valve resistance (R), The Pm at the beginning of inspiratory Row w as defined as the opening pressure (Pop), The Pth was constant through out inspiration, Pop was linearly related to Pth (p<0,0001, with slope s within 2% of identity and intercepts within +/-0.2 cmH(2)O, R was be tween 0.7-1.1 cmH(2)O . L-1 . s(-1) under all conditions and was indep endent of both Pth (p=0.76) and inspiratory Row (p=0.24), The results demonstrate that this system can provide a constant inspiratory thresh old load throughout inspiration with little Bow resistance, and is the refore ideal for respiratory studies.